Novel fuel cell cathodes and their fuel cells

ABSTRACT

Fuel cell cathodes and instant startup fuel cells employing the cathodes. The cathodes operate through the valency change mechanism of redox couples which uniquely provide multiple degrees of freedom in selecting the operating voltages available for such fuel cells. Such cathodes provide the fuel cells in which they are used a “buffer” or “charge” of oxidizer available within the cathode at all times.

RELATED APPLICATIONS

[0001] The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 10/185,414, which is assigned to the same assigneeas the current application, entitled “FUEL CELL CATHODE WITH REDOXCOUPLE”, filed Jun. 28, 2002, which is a continuation-in-part of U.S.Pat. No. 6,620,539, which is assigned to the same assignee as thecurrent application, entitled “Novel Fuel Cell Cathodes and Their FuelCells”, filed Mar. 1, 2001, the disclosure of which is herebyincorporated by reference.

FIELD OF THE INVENTION

[0002] The instant invention relates to generally to useful cathodesactive materials for fuel cells, more specifically to their use as thecathode material for instant startup alkaline fuel cells. Theseinventive cathodes open up a tremendous number of degrees of freedom infuel cell design by utilizing the change in valency states viareduction/oxidation of the cathode active material.

BACKGROUND OF THE INVENTION

[0003] The instant application for the first time provides cathodes, andfuel cells using such electrodes, which use oxide couples to yield awide selection of operating voltages. Specifically, the instantinventors have determined materials, when used in combination withhydrogen electrodes including hydrogen storage material, yield highperformance fuel cells. The high performance fuel cells have hydrogenstorage capacity within the hydrogen electrode and cathodes which takeadvantage of low-cost, in comparison with the traditional platinumelectrodes, oxide couples which allow selection of specific ranges ofoperating voltage of the electrochemical cells with a broad operatingtemperature range and the opportunity to provide instant-start by use ofthe hydrogen storage capability of the short-range order available inthe material of the hydrogen electrode.

[0004] As the world's human population expands, greater amounts ofenergy are necessary to provide the economic growth all nations desire.The traditional sources of energy are the fossil fuels which, whenconsumed, create significant amounts of carbon dioxide as well as othermore immediately toxic materials including carbon monoxide, sulfuroxides, and nitrogen oxides. Increasing atmospheric concentrations ofcarbon dioxide are warming the earth; creating the ugly specter ofglobal climatic changes. Energy-producing devices which do notcontribute to such difficulties are needed now.

[0005] A fuel cell is an energy-conversion device that directly convertsthe energy of a supplied gas into an electric energy. Highly efficientfuel cells employing hydrogen, particularly with their simple combustionproduct of water, would seem an ideal alternative to current typicalpower generations means. Researchers have been actively studying suchdevices to utilize the fuel cell's potential high energy-generationefficiency.

[0006] The base unit of the fuel cell is a cell having a cathode, ananode, and an appropriate electrolyte. Fuel cells have many potentialapplications such as supplying power for transportation vehicles,replacing steam turbines and power supply applications of all sorts.Despite their seeming simplicity, many problems have prevented thewidespread usage of fuel cells.

[0007] Presently most of the fuel cell R & D is focused on P.E.M.(Proton Exchange Membrane) fuel cells. Regrettably, the P.E.M. fuel cellsuffers from relatively low conversion efficiency and has many otherdisadvantages. For instance, the electrolyte for the system is acidic.Thus, noble metal catalysts are the only useful active materials for theelectrodes of the system. Unfortunately, not only are the noble metalscostly, they are also susceptible to poisoning by many gases,specifically carbon monoxide (CO). Also, because of the acidic nature ofthe P.E.M fuel cell electrolyte, the remainder of the materials ofconstruction of the fuel cell need to be compatible with such anenvironment, which again adds to the cost thereof. The proton exchangemembrane itself is quite expensive, and because of it's low protonconductivity at temperatures below 80° C., inherently limits the powerperformance and operational temperature range of the P.E.M. fuel cell asthe PEM is nearly non-functional at low temperatures. Also, the membraneis sensitive to high temperatures, and begins to soften at 120° C. Themembrane's conductivity depends on water and dries out at highertemperatures, thus causing cell failure. Therefore, there are manydisadvantages to the P.E.M. fuel cell which make it somewhat undesirablefor commercial/consumer use.

[0008] The conventional alkaline fuel cell has some advantages overP.E.M. fuels cells in that they have higher operating efficiencies, theyuse less costly materials of construction, and they have no need forexpensive membranes. The alkaline fuel cell also has relatively higherionic conductivity in the electrolyte, therefore it has a much higherpower capability. While the conventional alkaline fuel cell is lesssensitive to temperature than the PEM fuel cell, the platinum activematerials of conventional alkaline fuel cell electrodes become veryinefficient at low temperatures. Unfortunately, conventional alkalinefuel cells still suffer from their own disadvantages.

[0009] For example, conventional alkaline fuel cells still use expensivenoble metal catalysts in both electrodes, which, as in the P.E.M. fuelcell, are susceptible to gaseous contaminant poisoning. The conventionalalkaline fuel cell is also susceptible to the formation of carbonatesfrom CO₂ produced by oxidation of the anode carbon substrates orintroduced via impurities in the fuel and air used at the electrodes.This carbonate formation clogs the electrolyte/electrode surface andreduces/eliminates the activity thereof. The invention described hereineliminates this problem from the anode.

[0010] Fuel cells, like batteries, operate by utilizing electrochemicalreactions. Unlike a battery, in which chemical energy is stored withinthe cell, fuel cells generally are supplied with reactants from outsidethe cell. Barring failure of the electrodes, as long as the fuel,preferably hydrogen, and oxidant, typically air or oxygen, are suppliedand the reaction products are removed, the cell continues to operate.

[0011] Fuel cells offer a number of important advantages over internalcombustion engine or generator systems. These include relatively highefficiency, environmentally clean operation especially when utilizinghydrogen as a fuel, high reliability, few moving parts, and quietoperation. Fuel cells potentially are more efficient than otherconventional power sources based upon the Carnot cycle.

[0012] The major components of a typical fuel cell are the anode forhydrogen oxidation and the cathode for oxygen reduction, both beingpositioned in a cell containing an electrolyte (such as an alkalineelectrolytic solution). Typically, the reactants, such as hydrogen andoxygen, are respectively fed through a porous anode and cathode andbrought into surface contact with the electrolytic solution. Theparticular materials utilized for the cathode and anode are importantsince they must act as efficient catalysts for the reactions takingplace.

[0013] In an alkaline fuel cell, the reaction at the anode occursbetween the hydrogen fuel and hydroxyl ions (OH⁻) present in theelectrolyte, which react to form water and release electrons:

H₂+2OH⁻->2H₂O+2e ⁻ E₀=−0.828 v.

[0014] At the cathode, the oxygen, water, and electrons react in thepresence of the cathode catalyst to reduce the oxygen and form hydroxylions (OH⁻):

O₂+2H₂O+4e ⁻->4OH⁻ E₀=−0.401 v.

[0015] The total reaction, therefore, is:

2H₂═O₂->2 2H₂O E₀=−1.229 v

[0016] The flow of electrons is utilized to provide electrical energyfor a load externally connected to the anode and cathode.

[0017] It should be noted that the anode catalyst of the alkaline fuelcell is required to do more than catalyze the reaction of H⁺ ions withOH⁻ ions to produce water. Initially the anode must catalyze andaccelerate the formation of H⁺ ions and e⁻ from H₂. This occurs viaformation of atomic hydrogen from molecular hydrogen. The overallreaction may be simplified and presented (where M is the catalyst) as:

M+H₂->2M . . . H->M+2H⁺+2e ⁻.

[0018] Thus the anode catalyst must not only efficiently catalyze theelectrochemical reaction for formation of water at the electrolyteinterface but must also efficiently dissociate molecular hydrogen intoatomic hydrogen. Using conventional anode material, the dissociatedhydrogen is transitional and the hydrogen atoms can easily recombine toform hydrogen if they are not used very efficiently in the oxidationreaction. With the hydrogen storage anode materials of the inventiveinstant startup fuel cells, hydrogen is stored in hydride form as soonas they are created, and then are used as needed to provide power.

[0019] In addition to being catalytically efficient on both interfaces,the catalytic material must be resistant to corrosion by the alkalineelectrolyte. Without such corrosion resistance, the electrode wouldquickly succumb to the harsh environment and the cell would quickly loseefficiency and die.

[0020] One prior art fuel cell anode catalyst is platinum. Platinum,despite its good catalytic properties, is not very suitable for widescale commercial use as a catalyst for fuel cell anodes, because of itsvery high cost, availability, and the limited world supply. Also, noblemetal catalysts like platinum, also cannot withstand contamination byimpurities normally contained in the hydrogen fuel stream. Theseimpurities can include carbon monoxide which may be present in hydrogenfuel or contaminants contained in the electrolyte such as the impuritiesnormally contained in untreated water including calcium, magnesium,iron, and copper.

[0021] The above contaminants can cause what is commonly referred to asa “poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the anode. The catalyticefficiency of the anode therefore is reduced since the overall number ofavailable catalytically active sites is significantly lowered bypoisoning. In addition, the decrease in catalytic activity results inincreased over-voltage at the anode and hence the cell is much lessefficient adding significantly to the operating costs. Overvoltage isthe difference between the actual working electrode potential under someconditions and it's equilibrium value, the physical meaning ofovervoltage is the voltage required to overcome the resistance to thepassage of current at the surface of the anode (charge transferresistance). The overvoltage represents an undesirable energy loss whichadds to the operating costs of the fuel cell.

[0022] In related work, U.S. Pat. No. 4,623,597 (“the '597 patent”) andothers in it's lineage, the disclosure of which is hereby incorporatedby reference, one of the present inventors, Stanford R. Ovshinsky,described disordered multi-component hydrogen storage materials for useas negative electrodes in electrochemical cells for the first time. Inthis patent, Ovshinsky describes how disordered materials can be tailormade (i.e., atomically engineered) to greatly increase hydrogen storageand reversibility characteristics. Such disordered materials areamorphous, microcrystalline, intermediate range order, and/orpolycrystalline (lacking long range compositional order) wherein thepolycrystalline material includes topological, compositional,translational, and positional modification and disorder. The frameworkof active materials of these disordered materials consist of a hostmatrix of one or more elements and modifiers incorporated into this hostmatrix. The modifiers enhance the disorder of the resulting materialsand thus create a greater number and spectrum of catalytically activesites and hydrogen storage sites.

[0023] The disordered electrode materials of the '597 patent were formedfrom lightweight, low cost elements by any number of techniques, whichassured formation of primarily non-equilibrium metastable phasesresulting in the high energy and power densities and low cost. Theresulting low cost, high energy density disordered material allowed thebatteries to be utilized most advantageously as secondary batteries, butalso as primary batteries.

[0024] Tailoring of the local structural and chemical order of thematerials of the '597 patent was of great importance to achieve thedesired characteristics. The improved characteristics of the anodes ofthe '597 patent were accomplished by manipulating the local chemicalorder and hence the local structural order by the incorporation ofselected modifier elements into a host matrix to create a desireddisordered material. Disorder permits degrees of freedom, both of typeand of number, within a material, which are unavailable in conventionalmaterials. These degrees of freedom dramatically change a materialsphysical, structural, chemical and electronic environment. Thedisordered material of the '597 patent have desired electronicconfigurations which result in a large number of active sites. Thenature and number of storage sites were designed independently from thecatalytically active sites.

[0025] Multiorbital modifiers, for example transition elements, provideda greatly increased number of storage sites due to various bondingconfigurations available, thus resulting in an increase in energydensity. The technique of modification especially providesnon-equilibrium materials having varying degrees of disorder providedunique bonding configurations, orbital overlap and hence a spectrum ofbonding sites. Due to the different degrees of orbital overlap and thedisordered structure, an insignificant amount of structuralrearrangement occurs during charge/discharge cycles or rest periodsthere between resulting in long cycle and shelf life.

[0026] The improved battery of the '597 patent included electrodematerials having tailor-made local chemical environments which weredesigned to yield high electrochemical charging and dischargingefficiency and high electrical charge output. The manipulation of thelocal chemical environment of the materials was made possible byutilization of a host matrix which could, in accordance with the '597patent, be chemically modified with other elements to create a greatlyincreased density of electro-catalytically active sites and hydrogenstorage sites.

[0027] The disordered materials of the '597 patent were designed to haveunusual electronic configurations, which resulted from the varying3-dimensional interactions of constituent atoms and their variousorbitals. The disorder came from compositional, positional andtranslational relationships of atoms. Selected elements were utilized tofurther modify the disorder by their interaction with these orbitals soas to create the desired local chemical environments.

[0028] The internal topology that was generated by these configurationsalso allowed for selective diffusion of atoms and ions. The inventionthat was described in the '597 patent made these materials ideal for thespecified use since one could independently control the type and numberof catalytically active and storage sites. All of the aforementionedproperties made not only an important quantitative difference, butqualitatively changed the materials so that unique new materials ensued.

[0029] Disorder can be of an atomic nature in the form of compositionalor configurational disorder provided throughout the bulk of the materialor in numerous regions of the material. The disorder also can beintroduced by creating microscopic phases within the material whichmimic the compositional or configurational disorder at the atomic levelby virtue of the relationship of one phase to another. For example,disordered materials can be created by introducing microscopic regionsof a different kind or kinds of crystalline phases, or by introducingregions of an amorphous phase or phases, regions of an amorphous phaseor phases in addition to regions of a crystalline phase or phases. Theinterfaces between these various phases can provide surfaces which arerich in local chemical environments which provide numerous desirablesites for electrochemical hydrogen storage.

[0030] These same principles can be applied within a single structuralphase. For example, compositional disorder is introduced into thematerial which can radically alter the material in a planned manner toachieve important improved and unique results, using the Ovshinskyprinciples of disorder on an atomic or microscopic scale.

[0031] Additionally, in copending U.S. application Ser. No. 09/524,116,('116), the disclosure of which is hereby incorporated by reference,Ovshinsky has employed the principles of atomic engineering to tailormaterials which uniquely and dramatically advance the fuel cell art. Theinvention of '116 application has met a need for materials which allowfuel cells to startup instantaneously by providing an internal source offuel, to operate in a wide range of ambient temperatures to which a fuelcell will be exposed to under ordinary consumer use and to allow thefuel cell to be run in reverse as an electrolyzer therebyutilizing/storing recaptured energy. The anodes of the '116 fuel cellsare formed from relatively inexpensive hydrogen storage materials whichare highly catalytic to the dissociation of molecular hydrogen and theformation of water from hydrogen and hydroxyl ions as well as beingcorrosion resistant to the electrolyte, resistant to contaminantpoisoning from the reactant stream and capable of working in a widetemperature range.

[0032] The next step in the evolution of the fuel cell would be to findsuitable materials to replace the expensive platinum cathode catalystsof conventional fuel cells. It would also be advantageous to provide thecathode with the ability to store chemical energy (possibly in the formof chemically bound oxygen) to assist in the instant startup of the fuelcell as well as recapture energy Thus there is a need within the art forsuch a material. The invention described this application is significantin that it provides the next step in the development of suchelectrochemical cells. With this invention, the cathode can be selectedfrom a broad menu of available possible redox couples. These redoxcouples in addition to providing a store of chemical energy, allow theoperating voltage of the fuel cell to be selected, by judicious choiceof the redox couple used.

SUMMARY OF THE INVENTION

[0033] The present invention discloses cathodes utilizing a novelcathode active material. When utilized in fuel cell cathodes, thecathode active material provides the fuel cell with the ability to startup instantly and accept recaptured energy such as that of regenerativebraking by operating in reverse as an electrolyzer. The instant startupfuel cells have increased efficiency and power availability (highervoltage and current) and a dramatic improvement in operating temperaturerange (−20 to 150° C.) The fuel cells of the instant invention also haveadditional degrees of freedom over the fuel cells of the prior art inthat the voltage output of the cell can be tailored and they are capableof storing regenerated energy.

[0034] The cathodes of the present invention operate through themechanism of valency change reactions which uniquely provide multipledegrees of freedom in selecting the operating voltages available forsuch fuel cells. Such cathodes provide the fuel cells in which they areused, particularly alkaline fuel cells, with a level of chemical energystorage within the cathode itself. This means that such fuel cells willhave a “buffer” or “charge” available within the cathode at all times.

[0035] The cathode in accordance with the present invention comprises acathode active material including a valency change material. The valencychange material provides the cathode with an oxygen storage capacity.The valency change material may be a nickel hydroxide/nickeloxyhydroxide redox couple, a metal/metal oxide redox couple of anelement selected from copper, silver, zinc and cadmium, a metaloxide/oxide redox couple of a metal such as manganese, or a cobalthydroxide/oxyhydroxide redox couple.

[0036] The cathode may further include a hydrophobic component such aspolytetrafluoroethylene (PTFE). The hydrophobic component may be a)intimately mixed with the cathode active material, b) graded within thecathode active material, or c) a separate layer within the cathode. Thecathode may further include a current collector extending within thecathode active material. The current collector may comprise anelectrically conductive mesh, grid, foam or expanded metal. The furtherincluding a catalytic carbon component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1A is a stylized schematic depiction of a fuel cell anodeused in the fuel cells of the instant invention;

[0038]FIG. 1B is a stylized schematic depiction of an inventive fuelcell cathode used in the fuel cells of the instant invention;

[0039]FIG. 2 is a stylized schematic depiction of the instant startupalkaline fuel cell with hydrogen storage anode and oxide couple cathodein a preferred embodiment of the instant invention;

[0040]FIG. 3a is a plot of electrode potential (volts) of the cathodeversus the current density (mA/cm²) for both the redox cathode of theinstant invention and the comparative cathode;

[0041]FIG. 3b is a plot of percentage improvement of the voltage(reduction of polarization of the electrode) of the inventive cathodeover the comparative cathode versus the current density (mA/cm²);

[0042]FIG. 4 is a stylized schematic depiction of an energy supplysystem incorporating the instant startup alkaline fuel cell of apreferred embodiment of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0043] The present invention relates to cathodes for fuel cells whichoperate through the mechanism of valency change reactions of redoxcouples. The mechanism of valency change reactions uniquely providesmultiple degrees of freedom in selecting the operating voltagesavailable for such fuel cells by selecting from the many variable andreversible redox couples available. Such cathodes, or cathodes, providethe fuel cells in which they are used, particularly alkaline fuel cells,with a level of electrochemical energy storage via a change in valencystate within the cathode itself. This means that such fuel cells willhave a “buffer” or “charge” of reactant available within the cathode atall times which, particularly combined with hydrogen storage anodesdescribed in copending U.S. application Ser. No. 09/524,116 (thedisclosure of which is hereby incorporated by reference), yield instantstart fuel cells in general and more specifically to instant startalkaline fuel cells. Such fuel cells have a built in reserve of hydrogenwithin the anode and cathode reactant (possibly oxygen) in the cathodefor instant startup (discussed herein below), and have the ability toaccept the energy of regenerative braking by acting as an electrolyzer(also discussed herein below). The fuel cell has increased efficiencyand increased power capabilities as compared with conventional fuelcells of the prior art, while dramatically increasing the operatingtemperature range of the cell (−20 to 150° C.) The fuel cell is easy toassemble and has the advantage of utilizing proven, low cost productiontechniques.

[0044] The present invention also relates to fuel cell anodes andcathodes, and an energy supply system incorporating the present fuelcell. The fuel cell anode includes materials which have inherentcatalytic activity as well as hydrogen storage capacity. The cathode andanode materials do not include any noble metals, and are thereforeinherently low cost. The cathode and anode materials are robust andlong-lived, being resistant to poisoning. The anode does not utilize thecarbon substrates of the prior art. While a detailed discussion of theinstant electrodes and their utilization in an alkaline fuel cell isdescribed herein below, it should be noted that the concepts of theinstant invention can be applied to other types of fuel cells (e.g.P.E.M. fuel cells or metal-air cells).

[0045] In general, for such fuel cell cathodes, oxygen is generallyavailable to the cathode on a continuously-supplied basis on one side ofthereof where the catalytically active material converts the molecularoxygen into atomic oxygen which then migrates through the electrode andis reduced at the electrolyte interface of the cathode to form hydroxylions. In prior art cathodes, no storage of reactant occurs. That isoxygen travels directly through the active materials and reacts at theelectrolyte interface. In the cathodes of the instant invention, oxygenis stored in the cathode via a change in valency state within thereversible redox couples, and is then available, at the electrolyteinterface of the cathode. Available electrons will then be generatedthrough the electrochemical reaction with the fuel. Thus the fuel cellwill provide a constant supply of electricity at voltages based on thevalency change of the reversible redox couple being used (e.g. a metaland its oxide). Additionally, this added benefit may be obtained via achange in valency state in redox couples other than a metal and itsoxidized form. An example of this is the redox couple of nickelhydroxide/nickel oxyhydroxide or cobalt hydroxide/oxyhydroxide. Suchvalency changes may also occur between two different oxides of a metal,such as manganese or tin. In these types of systems, the electrochemicalcell will provide a potential whose theoretical voltage limit is the sumof the anode and cathode reactions. Certainly the theoretical limit ofvoltage available is modified or limited by other considerations, whichmay include the internal resistance of the electrodes and the completefuel cell system.

[0046] This invention specifically relates to a fuel cell cathodecomprising a cathode active material capable of reversibly storingenergy through a valency change mechanism of a redox couple. The cathodeactive material may have a first surface region situated to be exposedto molecular oxygen. The first surface region including a catalyticallyacting component promoting the absorption of molecular oxygen throughsaid first surface region and conversion thereof into atomic oxygen. Theactive material also includes a redox couple material (e.g. a metal)which is thereafter chemically charged by reaction with the atomicoxygen resulting in a valency change. The fuel cell cathode alsoincludes a second surface region situated to be exposed to a fuel cellelectrolyte. The second surface region includes a catalytic componentpromoting the valency change reactions between the redox active materialand the electrolyte. The cathode may also include a hydrophobiccomponent positioned between the first and second surface regions. Sucha fuel cell cathode will display favorable voltage potential overconventional prior art cathodes.

[0047] The fuel cell cathodes of this invention may utilize valencychange redox couples, particularly metal/oxides couples of metalsselected from copper, silver, zinc, cobalt and cadmium, metaloxide/oxide couples of metals selected from manganese or tin, or anickel hydroxide/nickel oxyhydroxide couple or a cobalthydroxide/oxyhydroxide couple.

[0048] The fuel cell cathodes of the instant invention also include acatalytic material which promotes and speeds the dissociation ofmolecular oxygen into atomic oxygen (which reacts with the redoxcouple). A particularly useful catalyst is carbon. As discussed hereinbelow this carbon should be very porous and may be electricallyconductive.

[0049] The cathode also needs a barrier means to isolate theelectrolyte, or wet, side of the cathode from the gaseous, or dry, sideof the cathode. A beneficial means of accomplishing this is by inclusionof a hydrophobic component comprising a halogenated organic compound,particularly polytetrafluoroethylene (PTFE) within the electrode.

[0050] These fuel cell cathodes, may also include a current collector orcurrent collecting system extending within said active material. Asdiscussed herein below, the current collector may comprise anelectrically conductive mesh, grid, foam or expanded metal. The choiceof such collection systems may be made according to electrodemanufacturing or production system needs.

[0051] Fuel cells of the instant invention using cathodes with valencychange redox couples, particularly in combination with the hydrogenstorage anodes of the '116 application provided the ability to recapturereverse electrical power flow from an external circuit into said fuelcell, electrolytically producing hydrogen and oxygen which are absorbedand stored through the mechanism of valency change reactions within theredox couple in the cathode and the hydrogen storage material in theanode.

[0052] Such fuel cells may, as a system, further comprise an electrolyteconditioning means for conditioning the electrolyte. This electrolyteconditioning system will not only adjust the temperature of theelectrolyte (for optimal fuel cell performance) but will also removewater from the electrolyte. The water removal is necessary because wateris produced as a by-product of the fuel cell's electrochemicalcombustion. This water, if not removed would dilute the electrolyte,thus impeding the optimal performance of the fuel cell.

[0053] These fuel cells will further include, as a system, a hydrogensupply source including means for continuously supplying fuel,particularly molecular hydrogen, to the anode's first surface region; anoxygen supply source which includes means for continuously supplyingmolecular oxygen to the cathode's first surface region; and anelectrolyte conditioning system which includes means for continuouslyconditioning the electrolyte, thereby enabling continuous operation ofthe fuel cell as an electrical power source.

[0054] Numerous valency change redox couples exist and may be used toform the cathode of this invention. When such couples are used, cyclingtransition from one valency state (the oxidized form) to another valencystate (the reduced form) is accomplished repeatedly and continuously.From a practical point of view, the ability to withstand such cycling ispreferred. While not wishing to be bound by theory, the inventorsbelieve that the equations representing some of the many availablereactions for the oxygen side of the fuel cell are presented below.

Co⁺²<------->Co⁺³ (Valency level 2 to a valency level 3)Co(OH)₂+OH⁻-->CoOOH+H₂O+e ⁻  (1)

Co⁺²<------->Co⁺⁴ (Valency level 2 to a valency level 4)Co(OH)₂+2OH⁻-->Co(OH)₄+2e ⁻ Co(OH)₄-->CoO₂+2H₂O  (2)

Ni⁺²<------->Ni⁺³ (Valency level 2 to valency level 3)Ni(OH)₂+OH⁻-->NiOOH+H₂O+e ⁻  (3)

Ni⁺²<------->Ni⁺⁴ (Valency level 2 to valency level 4)Ni(OH)₂+2OH⁻-->Ni(OH)₄+2e ⁻ Ni(OH)₄-->NiO₂+2H₂O  (4)

Ag<------->Ag⁺ (Valency level 0 to valency level 1)2Ag+2OH⁻-->Ag₂O+H₂O+e ⁻  (5)

Ag<------->Ag⁺² (Valency level 0 to valency level 2)Ag+2OH⁻-->AgO+H₂O+2e ⁻  (6)

Cu<------->Cu⁺² (Valency level 0 to valency level 2)Cu+2OH⁻-->CuO+H₂O+2e ⁻  (7)

(Ni/Ag)⁺²<------->(Ni/Ag)  (8)

(Ni/Fe) oxide⁺²<------->(Ni/Fe)oxide⁺³  (9)

Mn⁺²<---->Mn⁺³----->Mn⁺⁷  (10)

Sn⁺²<---->Sn⁺⁴  (11)

[0055] Groups 8, 9, 10, and 11 are comprised of multiple elements havingmultiple valency states. The multiple valency states may createdifficulty in predicting which reaction is predominant in each grouping.

[0056] As noted earlier, the previous sets of reactions provide a fewexemplary valency change reactions which will be useful for the air oroxygen side of fuel cells using the cathodes of this invention. Theseexamples are provided simply to demonstrate useful couples; the listcertainly is not exhaustive, nor is it intended to be so. Many othervalency change redox couples are available and will have usefulapplication in the inventive oxygen-side electrodes which are, in turn,useful in the described inventive fuel cells.

[0057] Quantifying the useful benefits of a few of these couples itshould be noted that use of the copper/copper oxide couple will yieldvoltage of about 0.8 v per cell; silver/silver (+2 oxidation state)oxide will yield voltage of about 0.9 v per cell; nickeloxyhydroxide/nickel hydroxide will yield voltage of about 1 v per cell.It should also be considered that there are a number of complex oxideswhich will yield differing cell voltages which expands the availableworking voltages even further. Nickel ferrate (NiFeO₄) is one such oxidewhose complex is available to be used and whose voltage contributionwould be about 1 volt. This and other “mixed” oxide complexes provideother useful voltage opportunities as part of this invention. The nickeloxyhydroxide/hydroxide which was previously discussed is, effectively,another complex oxide system. Some of these offer unique multi-stepreactions which may be advantageously applied in the practice of thisinvention.

[0058] At the cathode, the oxygen, water, and electrons react in thepresence of the cathode active material to reduce the oxygen and formhydroxyl ions (OH⁻):

O₂+2H₂O+4e ⁻→4OH⁻.

[0059] The flow of electrons is utilized to provide electrical energyfor a load externally connected to the anode and cathode. That load isavailable to be filled by any number of needs including, but not limitedto, powering motive vehicles, lighting devices, heating or coolingdevices, power tools, entertainment devices, and otherelectricity-consuming devices too numerous to mention.

[0060] In a fuel cell, the cathodes just described (employing any of themany valency change redox couples) are used in conjunction with an anodeor hydrogen electrode. While any functional hydrogen electrode may beused with the inventive cathodes, preferred embodiments of the fuelcells of this invention will include anodes employing hydrogen storagealloy active materials. It should be noted that the preferred anodecatalyst of the alkaline fuel cell is required to do more than catalyzethe reaction of H⁺ ions with OH⁻ ions to produce water. Initially theanode must catalyze and accelerate the formation of H⁺ ions and e⁻ fromH₂. This occurs via formation of atomic hydrogen from molecularhydrogen. The overall reaction can be seen as (where M is the hydrogenstorage anode active alloy material):

M+H₂→M . . . H→MH→M+H⁺ +e ⁻.

[0061] That is, molecular hydrogen (H₂) is converted to adsorbed atomichydrogen (M . . . H) onto the surface of the anode. This adsorbedhydrogen is very quickly converted to a metal hydride (MH) in the bulkof the hydrogen storage alloy. This hydride material is then convertedto ionic H⁺ releasing an electron e⁻. The ionic hydrogen reacts with ahydroxyl ion in the electrolyte to produce water and the electron isreleased into the external load circuit. Thus the anode catalyst mustnot only efficiently catalyze the formation of water at the electrolyteinterface, but must also efficiently dissociate molecular hydrogen intoionic hydrogen. Using conventional anode material, the dissociatedhydrogen is transitional and the hydrogen atoms can easily recombine toform hydrogen if they are not used very quickly in the oxidationreaction. With hydrogen storage anode materials, hydrogen is trapped inhydride form as soon as hydrides are created. The hydrogen, aselectrochemically released into the electrolyte, are then used as neededto provide the fuel cell's electrical power output.

[0062] In addition to being catalytically efficient on both interfaces,the catalytic material must be resistant to corrosion by the alkalineelectrolyte. Without such corrosion resistance, the electrode wouldquickly succumb to the harsh environment and the cell would quickly loseefficiency and die.

[0063] One prior art fuel cell anode catalyst is platinum. Platinum,despite its good catalytic properties, is not very suitable for widescale commercial use as a catalyst for fuel cell anodes, because of itsvery high cost. Also, noble metal catalysts like platinum cannotwithstand contamination by impurities normally contained in the hydrogenfuel stream. These impurities can include carbon monoxide (which may bepresent in hydrogen fuel) or contaminants contained in the electrolytesuch as the impurities normally contained in untreated water such ascalcium, magnesium, iron, and copper.

[0064] The above contaminants can cause what is commonly referred to asa “poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the anode. The catalyticefficiency of the anode therefore is reduced since the overall number ofavailable catalytically active sites is significantly lowered bypoisoning. In addition, the decrease in catalytic activity results inincreased overvoltage at the anode making the cell much less efficientresulting in an increase to the operating costs. Overvoltage is thedifference between the electrode potential and it's equilibrium value,the physical meaning of over-voltage is the voltage required to overcomethe resistance to the passage of current at the surface of the anode(charge transfer resistance). The overvoltage represents an undesirableenergy loss which adds to the operating costs of the fuel cell.

[0065] Without intending to limit the true scope of this invention, butrather for the purpose of explanation and making the current inventionmore understandable, explanatory drawings are provided. FIGS. 1A and 1Bare stylized schematic depictions of a fuel cell storage electrodes 1 aand 1 c (“a” designates anode and “c” designates cathode). The anode 1 apreferably comprises a hydrogen storage active material and the cathodepreferably comprises a cathode active material including a valencychange redox couple. The electrode body includes, in a preferredembodiment a hydrophobic component 2 a (anode) and 2 c (cathode). Thehydrophobic component may be polytetrafluoroethylene (PTFE). Theelectrodes also include either a region comprising hydrogen storageactive material 3 a for the anode, or a region comprising at least onevalency change redox couple 3 c for the cathode. While FIGS. 1A and 1Bshow the hydrophobic component 2 a, 2 c and the active electrodematerial component 3 a, 3 c as separate layers of material within theelectrodes 1 a, 1 c, they may also be intimately mixed into a singlematerial or graded throughout the active material. The electrodes 1 a, 1c also include a substrate component 4 a (anode) or 4 c (cathode), whichat least acts as a current collector, but may also provide a supportfunction. This substrate component is discussed herein below.

[0066] The electrodes 1 a, 1 c have two surfaces 5 a (anode) or 5 c(cathode), and 6 a (anode) or 6 c (cathode). One surface of eachelectrode 5 a, 5 c is adjacent a reactant (i.e. hydrogen or oxygen)which is usefully supplied by an inlet mechanism when incorporated intothe fuel cell, while the other surface 6 a, 6 c is adjacent to theelectrolyte (which in a preferred embodiment will be an aqueous alkalineelectrolyte). As stated above, the hydrophobic (PTFE) component 2 a, 2 cis either a layer within the electrodes or is intimately mixed with theactive material 3 a, 3 c. In either case, the purpose of the hydrophobic(PTFE) material is to act as a water barrier, preventing electrolyte orits diluent from escaping from the fuel cell, while at the same time,allowing either the fuel, preferably hydrogen (in the case of the anode)or the oxygen (in the case of the cathode) to pass from the sourcethereof to the electrode active material 3 a, 3 c. Thus, a portion ofthe electrode, surface 6 a, 6 c (and somewhat interiorly from thesurface) is in contact with the electrolyte and acts to oxidize(providing electrons) the fuel, preferably hydrogen in the anode case orreduce (gaining electrons) the oxidizer, preferably oxygen in thecathode case, while the remainder of the electrode material (includingsurface 5 a, 5 c) provides for dissociation of molecular hydrogen oroxygen and storage of the dissociated fuel (anode) or oxidizer (cathode)for later reaction at surface 6 a, 6 c.

[0067] In the drawings, the anode active material is a material, such asa platinum based active material or a hydrogen storage material. Thepreferable hydrogen storage alloy is one which can reversibly absorb andrelease hydrogen irrespective of the hydrogen storage capacity and has afast hydrogenation reaction rate, good stability in the electrolyte, anda long shelf-life. It should be noted that, by hydrogen storagecapacity, it is meant that the material stores hydrogen in a stableform, in some nonzero amount higher than mere trace amounts. Preferredmaterials will store about 0.1 weight % hydrogen or more. Preferably,the alloys include, for example, rare-earth/Misch metallic alloys,zirconium, and/or titanium alloys or mixtures thereof. The anodematerial may even be layered such that the material on the hydrogeninput surface 5 a is formed from a material which has been specificallydesigned to be highly catalytic to the dissociation of molecularhydrogen into atomic hydrogen, while the material on electrolyteinterface surface 6 a is designed to be highly catalytic to theformation of water from hydrogen and hydroxyl ions.

[0068] For the cathode, the active material is a composite of a selectedvalency change redox couple providing for oxygen storage via a valencychange and an additional catalytic material. Some preferable valencychange redox couples are discussed herein above. As general preferences,the valency change redox couple should reversibly absorb and releaseoxygen irrespective of the oxygen storage capacity and have a fastoxidation reaction rate, good stability in the electrolyte, and a longshelf-life. It should be noted that, by oxygen storage capacity, it ismeant that the material stores oxygen in a stable form via a valencychange reaction, in some nonzero amount higher than mere trace amounts.

[0069] In either case, for either electrode, the electrode material maybe layered such that the material on the fuel, or oxidizer, inputsurface 5 a, 5 c is formed from a material which has been specificallydesigned to be highly catalytic to the dissociation of either the fuelor the oxidizer, while the material on electrolyte interface surface 6a, 6 c is designed to be highly catalytic to the formation of water(anode) or hydroxyl ions (cathode). In addition to having exceptionalcatalytic capabilities, the materials also have outstanding corrosionresistance toward the electrolyte of the fuel cell.

[0070] In use, the anode (hydrogen electrode) alloy materials act as 1)a molecular hydrogen decomposition catalyst throughout the bulk of theanode; 2) as a water formation catalyst, forming water from hydrogen andhydroxyl ions (from the aqueous alkaline electrolyte) at surface 6 ofthe anode; and 3) as an internal hydrogen storage buffer to insure thata ready supply of hydrogen ions is always available at surface 6 (thiscapability is useful in situations such as fuel cell startup andregenerative energy recapture, discussed herein below).

[0071] Specific alloys useful as the anode material are alloys thatcontain enriched catalytic nickel regions of 50-70 Angstroms in diameterdistributed throughout the oxide interface which vary in proximity from2-300 Angstroms preferably 50-100 Angstroms, from region to region. As aresult of these nickel regions, the materials exhibit significantcatalysis and conductivity. The density of Ni regions in the alloy ofthe '591 patent provides powder particles having an enriched Ni surface.The most preferred alloys having enriched Ni regions are alloys havingthe following composition:

[0072] (Base Alloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e)

[0073] where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1to 40 atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomicpercent Ni, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic percent;c is 13 to 17 atomic percent; d is 0 to 3.5 atomic percent; e is 0 to1.5 atomic percent; and a+b+c+d+e=100 atomic percent.

[0074] The substrate component 4 a, 4 c acts as an electrical conductorand may usefully also act as a support means. For example, if a powderedelectrically conductive material, such as nickel, nickel alloy, copper,copper alloy or carbon, is mixed into the active material 3 a, 3 c thenthe material acts as an electrically conductive materials, but does notprovide any support for the electrode materials per se.

[0075] It is preferable that the substrate component act as both anelectrical conductor and a support structure. The electrode may beformed by pressing active material into a porous metal substrate. Theconductivity of the electrode can be increased by increasing theconductivity of the electrode's porous metal substrate. Generally theporous metal substrate includes, but is not limited to, meshes, grid,matte, foil, foam, plate, and expanded metal. Preferably, the porousmetal substrate used for the electrode is a mesh, grid, foam, orexpanded metal. The substrate may be formed from any material which iselectrically conductive and resistant to corrosion or chemical attack bythe electrolyte. Nickel or nickel alloy is a very good material, but forhigh power applications it may be too resistive. Thus when high power isrequired, the substrate is formed from copper, copper-plated nickel, ora copper-nickel alloy, as taught by U.S. Pat. No. 5,856,047 (Venkatesan,et al.) and U.S. Pat. No. 5,851,698 (Reichman et al.), the disclosuresof which are hereby incorporated by reference. As used herein, “copper”refers to either pure copper or an alloy of copper, and “nickel” refersto either pure nickel or an alloy of nickel. Using copper to form theporous metal substrate of the electrode has several importantadvantages. Copper is an excellent electrical conductor. Hence, its useas a substrate material decreases the resistance of the anode. Thisdecreases the amount of fuel cell power wasted due to internaldissipation, and thereby provides a fuel cell having increased outputpower. Copper is also a malleable metal. Increased substratemalleability allows the substrate to more reliably hold the activehydrogen storage material that is compressed onto the substrate surface.This lessens the need to sinter the electrode after the active materialhas been compressed onto the substrate, thereby simplifying and reducingthe cost of the anode manufacturing process.

[0076] The cathode contains an active material component which iscatalytic to the dissociation of molecular oxygen into atomic oxygenand/or catalytic to the formation of hydroxyl ions (OH⁻) and hydrogenfrom water, corrosion resistant to the electrolyte, and resistant topoisoning.

[0077] The cathode is formed in much the same manner as the anode or maybe formed in a manner similar to conventional cathodes which useplatinum catalysts, but the valency change redox couple materialsdescribed above are substituted for the platinum. The valency changeredox couple is finely divided and disbursed throughout a porous carbonmaterial. The carbon material may be in the form of a powder, matte,foam, grid or mesh. The cathode may or may not have a conductivesubstrate as needed. If used the substrate can be as described inrelation to the anode.

[0078] When the instant fuel cell is run in reverse, as an electrolyzer,during an energy recapture process such as regenerative braking, wateris electrolyzed into hydrogen and oxygen. That is, when electric poweredvehicles are used in stop and go mode in inner cities, regenerativebraking systems can recapture kinetic energy, and convert it toelectrical energy. In this mode, the electric motors reverse their rolesand become generators using up the kinetic energy of the motion. Thiscauses a spike of current which amounts to about 10% of the normaloperating load. A conventional fuel cell (alkaline or PEM) cannot acceptsuch surges. This feedback of energy would cause rapid hydrogen andoxygen evolution which would cause the catalysts to lose their integrityand adhesion thereby undermining the overall system performance.

[0079] In the inventive fuel cell, this will not be a problem, becausethe hydrogen storage anode and the valency change redox couple cathodewill take the surge current and become charged with the producedhydrogen or oxygen respectively.

[0080] It should be noted that the anode and cathode active materials ofthe instant invention are robust and very resistant to poisoning. Thisis true because the increased number of catalytically active sites ofthese materials not only increases catalytic activity, but enables thematerials to be more resistant to poisoning, because with materials ofthe present invention numerous catalytically active sites can besacrificed to the effects of poisonous species while a large number ofnon-poisoned sites still remain active to provide the desired catalysis.Also, some of the poisons are inactivated by being bonded to other siteswithout effecting the active sites.

[0081]FIG. 2 is a stylized schematic depiction of an alkaline fuel cell7 incorporating the electrodes 1 a, 1 c (“a” designates anode and “c”designates cathode) of the instant invention. The fuel cell 7 consistsof three general sections: 1) an anode section, which includes the anode1 a and a hydrogen supply compartment 8; 2) the electrolyte compartment11; and 3) the cathode section, which includes the cathode 1 c and theoxygen (air) supply compartment 10.

[0082] In the anode section, hydrogen or hydrogen containing gasmixtures is supplied under pressure to the hydrogen supply compartment 8through hydrogen inlet 12. Hydrogen is then absorbed through surface 5 ainto the anode 1 a. The absorbed hydrogen is catalytically broken downby the anode active material into atomic hydrogen which is stored in thehydrogen storage material as a hydride, and then finally reacts atsurface 6 a with hydroxyl ions to form water. It should be noted thatthe heat of hydride formation helps to warm the fuel cell to it'soptimal operating temperature. Any unabsorbed hydrogen and othercontaminant gases or water vapor in the hydrogen supply are ventedthrough outlet 13. The gases that are vented may be recycled if enoughhydrogen is present to warrant recovery. Otherwise the hydrogen may beused to provide a source of thermal energy if needed for othercomponents such as a hydride bed hydrogen storage tank.

[0083] The electrolyte compartment 11 holds (in this specific example)an aqueous alkaline electrolyte in intimate contact with the anode 1 aand the cathode 1 c. The alkaline solution is well known in the art andis typically a potassium hydroxide solution. The electrolyte provideshydroxyl ions which react with hydrogen ions at surface 6 a of the anode1 a and water molecules which react with oxygen ions at surface 6 c ofthe cathode 1 c. The electrolyte is circulated through compartment 11via inlet 14 and outlet 15 (in alternative embodiments, the electrolytemay be deliberately immobilized as by jelling, etc.) The circulatedelectrolyte may be externally heated or cooled as necessary, and theconcentration of the electrolyte can be adjusted (as via wicking, etc.)as needed to compensate for the water produced by the cell and anylosses due to evaporation of water through the electrodes. Systems forconditioning the fuel cell electrolyte are well known in the art andneed not be further described in detail herein.

[0084] In the cathode section, oxygen, air, or some other oxygencontaining gaseous mixture is supplied to the oxygen supply compartment10 through oxygen inlet 18. Oxygen is then absorbed through surface 5 cinto the cathode 1 c. The absorbed oxygen is catalytically broken downby the cathode active material into atomic oxygen, which finally reactsat surface 6 c (via the valency change mechanism of the redox couple)with water molecules to form hydroxyl ions. Any unabsorbed oxygen andother gases in the feed (e.g. nitrogen, carbon dioxide, etc.) or watervapor in the oxygen supply are vented through outlet 19.

EXAMPLE

[0085] Production of a hydrogen storage anode (used in both theinventive fuel cell and the control cell) is described as follows. Allpercentages given throughout this example are in weight percent, unlessotherwise noted. A mixture containing about 90% of a Mischmetal nickelalloy (having an approximate composition of 20.7% La, 8.5% Ce, 1.0% Pr.2.9% Nd, 49.9% Ni, 10.6% Co, 4.6% Mn, 1.8% Al) and about 10%polytetrafluoroethylene (PTFE) was made into a paste using isopropylalcohol. This paste was applied into an Inco Corporation nickel foamhaving a of density of about 500 g/m² (with a previously welded nickeltab used as a current collector). This foam acts as the substrate andelectrical collector for the electrode. After drying at 50-60° C., theanode was compacted using a roll mill to a final thickness of 0.020 to0.030 inches.

[0086] The control sample cathode (oxygen) electrode was created asfollows. First, a mixture of Vulcan XC-72 carbon (Trademark of CabotCorp.) and PTFE was prepared with an approximate PTFE content of 20-30%.Nickel foam of the type used above in the anode production was used as asubstrate. A paste (paste A) of the Vulcan XC-72 carbon/PTFE mixture wascreated using sufficient isopropyl alcohol to produce a workable paste.Paste A was then applied into one side (the electrode/gas interfaceside) of the foam substrate. A second paste (paste B), consisting of amixture of approximately of 40-60% of the Vulcan XC-72 carbon/PTFEmixture and a high surface area carbon (Black Pearls 2000, Trademark ofCabot Corp.) was created, again using sufficient isopropyl alcohol toproduce a workable paste. Paste B was applied into the other side (theelectrode/electrolyte interface side) of the foam. After drying theelectrode at 60-100° C., it was compacted to final thickness of 0.030 to0.040 inches by applying even pressure of 1 to 3 tons/cm².

[0087] The inventive electrode was created in a similar manner as thecomparative electrode except that 10% Aldrich silver oxide was added topaste B. The inventive cathode contains only about 0.11 grams of activesilver oxide redox material. This amount of silver oxide has anelectrochemical capacity of about 40 mAh. At a typical discharge rate of100 mA/sq.cm, the electrode would be discharged at a current of !A. Atthis current, the electrode should be fully discharged in 2.5 minutes ifthere is no continuous regeneration of the active ingredients. Also thecell voltage, which includes all polarizations, should reflect a highervalue if oxygen reduction were occurring by a redox mechanism as opposedto the conventional mechanism.

[0088] Fuel cells were created using the same anodes and respectivelyeither the control cathode or the inventive cathode. These fuel cellsincluded a 60 g/m² polypropylene separator from Daiwabo Corporation, andemployed conventional KOH/LiOH alkaline battery electrolyte which wasjelled using 3% carboxymethylcellulose. The cells were run usingpurified hydrogen as the fuel and air as the source of oxygen.

[0089]FIG. 3a is a plot of electrode potential (volts) of the cathodeversus the current density (mA/cm²) for both the inventive valencychange redox couple cathode (♦ symbol) and the comparative cathode (▪symbol). Each data point represents 5 minutes of discharge at thatparticular current density. Thus as can be seen, the electrode potentialfor the inventive cathode is always higher than that of the controlsample (at useful current densities) and as the current densityincreases (i.e. higher power) the voltage of the control sample dropsoff much more rapidly than that of the inventive cathode (which dropsonly slightly by comparison) FIG. 3b is a plot of percentage improvementof the voltage (reduction of polarization of the electrode) of theinventive cathode over the comparative cathode versus the currentdensity (mA/cm²). As may be seen from this graph, at useful currentdensities, the improvement in the polarization of the inventiveelectrode is anywhere from 30% to 50% over that of the comparativecathode. Thus, FIGS. 3a and 3 b show that the cell is fully capable ofoperating for longer than 2.5 minutes (the capacity base of only thesilver oxide in the cathode) and at a higher voltage than thecomparative cathode. Therefore, it is apparent that continuousreplenishment of oxygen into the silver oxide redox couple via a changein the valency state of the redox couple by the supplied air is beingaccomplished.

[0090] It should be noted that cathodes containing in the range of 1-20%by weight of silver oxide (in paste B) were produced. Cathodes havinglower amounts of silver oxide than the 10% in the cathode of the example(i.e. in the 1% range) showed the same effects, although somewhatdiminished. Cathodes produced with higher than the 10% silver oxide ofthe example cathode (i.e. about 20%) showed no increased effect over thesample cathode. Thus, the effective range appears bounded by a lowerlimit of about 0.5% silver oxide. The upper limit of silver oxideinclusion seems to only be bounded by factors such as cost and the needfor carbon to catalyze the reaction at the electrode/electrolyteinterface. This range limit, determined by empirical means, applies onlyto silver, and other redox couples will have their own limits on therange of inclusion which may be determined by similar simpleexperimental trials.

[0091]FIG. 4 is a stylized schematic depiction of an energy supplysystem incorporating the alkaline fuel cell 7 of the instant invention.The energy supply system also includes a source of hydrogen 20. Thesource may be of any known type, such as a hydride bed storage system, acompressed hydrogen storage tank, a liquid hydrogen storage tank, or ahydrocarbon fuel reformer. The preferred source is a metal hydridestorage system. The hydrogen from the source 20 is transported to thefuel cell 7 via input line 21, and excess gases are vented throughoutput line 22. A portion of the gases from output line 22 may berecycled to input line 21 through recycle line 32. The energy supplysystem also includes a source of oxygen, which is preferably air. Theair is drawn into line 33 and then can be passed through a carbondioxide scrubber 23. The air is then transported to the fuel cell 7 viainput line 24. Excess air and unused gases are vented through outputline 25. Since this gas stream contains no harmful gases, it may bevented to the environment directly.

[0092] The energy supply system also includes an electrolyterecirculation system. The electrolyte from the fuel cell 7 is removedthrough output line 28 and sent to an electrolyte conditioner 26. Theelectrolyte conditioner 26 heats or cools the electrolyte as needed andremoves/adds water as necessary. The conditioned electrolyte is thenreturned to the fuel cell 7 via input line 27.

[0093] Finally the energy supply system includes electrical leads 29 and30 which supply electricity from the fuel cell 7 to a load 31. The loadcan be any device requiring power, but particularly contemplated is thepower and drive systems of an automobile.

[0094] The instant fuel cell and energy supply systems incorporating itare particularly useful for applications in which instant start andenergy recapture are requirements thereof, such as for example inpowering a vehicle. For instance, in consumer vehicle use, a fuel cellthat has the built in hydrogen and oxygen storage of the instantinvention has the advantage of being able to start producing energyinstantly from the reactants stored in it's electrodes. Thus, there isno lag time while waiting for hydrogen to be supplied from externalsources. Additionally, because hydrogen and oxygen can be adsorbed andstored in the respective electrode materials of the fuel cell, energyrecapture can be achieved as well. Therefore, activities such asregenerative braking, etc., can be performed without the need for anbattery external to the fuel cell because any reactants produced byrunning the fuel cell in reverse will be stored in the electrodes of thefuel cell. Therefore, in essence, fuel cells employing the instantactive electrode materials are the equivalent of a fuel cell combinedwith a battery. In such a system employing the valency change redoxcouples, oxygen is able to be stored within the electrode via a changein the valency state of the redox couple to a significant degree. Suchcouples may be a metal/metal oxide couple, a hydroxide/oxyhydroxidecouple, a metal oxide/oxide couple, or combinations thereof.

[0095] The novel electrochemical cell of the present invention alsoenables the practice of the method of the invention which, in oneembodiment thereof, comprises the indirect and continuous introductionof both the fuel, preferably hydrogen, and the reactant which oxidizesthe fuel, preferably oxygen, for the continuous operation of theelectrochemical cell as a fuel cell. That is, the hydrogen is, duringoperation, continuously introduced through a catalytic region in thenegative electrode and continuously stored as a hydride in a region ofmaterial in the negative electrode which is capable of reversiblystoring and releasing hydrogen. Simultaneously, hydrogen iselectrochemically released from the electrolyte side of the negativeelectrode to participate in the cell reaction process while a continuoussupply of hydrogen at the gas side is stored within the anode replacingthe hydrogen reacted at the electrolyte side.

[0096] At the same time oxygen is continuously introduced at the gasside of the positive electrode through a catalytic region and chemicallystored via a valency change mechanism as a material in the form of thecharged state of an oxide couple which participates in the cellreaction. Simultaneously with the introduction and chemical storage ofthe oxygen as just explained the material of the valency change redoxcouple which is in the charged state participates in the cell reactionto generate electrical power. Thus an electrochemical cell iscontinuously operated through the supply to the gas side, storagewithin, and release from the electrolyte side of, the oxidant so thatoperation as a fuel cell is enabled. The unique method of the inventionof operation of an electrochemical cell as a fuel cell is thus madepossible. In the situations in which the fuel cell is run “backwards” oras an electrolyzer to recapture and store energy, such as for example,during regenerative braking, the operating nature as described earlierwould not be considered to be disruptive to “continuous” operation.

[0097] While there have been described what are believed to be thepreferred embodiments of the present invention, those skilled in the artwill recognize that other and further changes and modifications may bemade thereto without departing from the spirit of the invention, and itis intended to claim all such changes and modifications as fall withinthe true scope of the invention.

1. In a electrochemical cell, a cathode comprising: a cathode activematerial including a valency change material.
 2. The cathode accordingto claim 1, wherein said valency change material provides said cathodewith a cathode fuel storage capacity via a change in the valency stateof the valency change material.
 3. The cathode according to claim 1,wherein said valency change material provides said cathode with anoxygen storage capacity via a change in the valency state of the valencychange material.
 4. The cathode according to claim 1, wherein saidvalency change material is a nickel hydroxide/nickel oxyhydroxide redoxcouple.
 5. The cathode according to claim 1, wherein said valency changeredox material comprises a metal/metal oxide redox couple of an elementselected from the group consisting of copper, silver, zinc and cadmium.6. The cathode according to claim 1, wherein said valency change redoxmaterial comprises a metal oxide/oxide redox couple of a metal selectedfrom tin or manganese.
 7. The cathode according to claim 1, wherein saidvalency change redox material comprises a cobalt hydroxide/oxyhydroxideredox couple.
 8. The cathode of claim 1, further including a hydrophobiccomponent.
 9. The cathode of claim 8, wherein said hydrophobic componentcomprises polytetrafluoroethylene (PTFE).
 10. The cathode of claim 9,wherein said PTFE is at least one of: a) intimately mixed with saidcathode active material; b) graded within said cathode active material;or c) a separate layer within said cathode.
 11. The cathode of claim 1,further including a current collector extending within said activematerial.
 12. The cathode of claim 11 wherein said current collectorcomprises an electrically conductive mesh, grid, foam or expanded metal.13. The cathode of claim 1, further including a catalytic carboncomponent.
 14. A cathode active material for a cathode comprising: avalency change material adapted to store and supply a cathode fuel via achange in valency during use of said cathode.
 15. The cathode activematerial of claim 14, wherein said cathode fuel is oxygen.
 16. Thecathode active material according to claim 14, wherein said valencychange redox material is a nickel hydroxide/nickel oxyhydroxide redoxcouple.
 17. The cathode active material according to claim 14, whereinsaid valency change redox material comprises a metal/metal oxide redoxcouple of an element selected from the group consisting of copper,silver, zinc and cadmium.
 18. The cathode active material according toclaim 14, wherein said valency change redox material comprises a metaloxide/oxide redox couple of a metal selected from tin or manganese. 19.The cathode active material according to claim 14, wherein said valencychange redox material comprises a cobalt hydroxide/oxyhydroxide redoxcouple.